X-ray diffractometers are known in the art and are used for applications such as directing an x-ray beam toward a crystal to obtain reflection angles of the beam from the crystal for use in studying the crystal. The analysis of a crystal using an x-ray diffractometer can require a significant amount of time with eight hours to three days not being unusual. During the period of experimentation with a crystal, the shutter of the x-ray diffractometer may be opened and closed 10,000 to 15,000times in a 24-hour period.
In a conventional x-ray diffractometer, such as a Model No. AFC6, RU200B Series x-ray diffractometer from Rigaku Corporation of Japan, the shutter comprises a rotary controlled shutter element which is rotated between a first closed position and a second open position. When the shutter is open, a path is provided between a radiation source and a target, such as a crystal. In this apparatus, a solenoid is rotated to rotate a shaft which in turn rotate the shutter. A bar magnet is supported on the shaft and is shifted as the shaft rotates between a first position, corresponding to the closed position of the shutter, and a second position, corresponding to the open position of the shutter. As the shaft rotates between the respective first and second positions, reed switches at these positions are activated to provide a shutter position indicating signal.
In operation, a computer controller of the Rigaku device causes the solenoid to shift the shutter to a desired position, such as to the second or open position. The computer then receives a position indicating signal from one of the reed switches and compares this signal with the expected position corresponding to the position to which the shutter has been operated by the solenoid in response to the controller. If the expected position does not correspond to the detected position determined from the signals from the reed switches, a shutter error position signal is generated. In the case of a shutter error, the solenoid is operated to close the shutter and the system shuts down.
Because of the large number of shutter operations normally required during the analysis of a crystal or during other uses of the x-ray diffractometer, the reed switches tend to wear, with frequent component replacement being required. Also, proper alignment of the replacement reed switches is difficult to attain. Furthermore, as the parts deteriorate through use, false shutter position indicating signals are generated and result in the erroneous shutdown of the equipment. This results in a substantial loss of many hours of experimentation time, particularly when x-ray diffractometers are set up for the automatic running of an experiment overnight or on a weekend with a researcher returning and learning that the experiment has stopped midstream. In addition, sometimes valuable sample crystals are lost due to the instability of these crystals and the fact that these crystals lack the stability simply to restart an experiment which has erroneously been terminated.
The inventor has found that the Rigaku system as described above frequently provided false shutter position errors, with errors occurring at least once every three or four days over many periods of operation of the x-ray diffractometer.
This problem with accurately controlling and detecting the presence of a shutter under the adverse operating conditions required by an x-ray diffractometer have been present for a number of years. That is, since the Rigaku x-ray diffractometer mentioned above was introduced, the inventor understands that this problem of generating false shutter position signals has plagued users of this device without being solved. The assignee of the present invention first obtained this model of Rigaku x-ray diffractometer in November of 1987.
Therefore, a need exists for an improved shutter control mechanism for an x-ray diffractometer designed to overcome these and other problems of the prior art.